The chemical ecology of some British freshwater gastropod molluscs: behavioural responses to short chain carboxylic acids and maltose

The behavioural responses of 6 common British snails were monitored during 40 minutes exposure (using diffusion olefactometers) to concentration gradients of 5 short chain carboxylic acids (Carbon-2 to Carbon-5, Carbon-8) or maltose. Ranking on the basis of the total number of significant responses recorded was Limnaea peregra (17), Planorbis contortus (15), Physa fontinalis (12), Planorbis planorbis (11), Bithynia tentaculata (4), and Planorbis vortex (1). There was no correlation between snail activity indices and the number of significant responses, indicating that results reflected true differences in chemoreception. L. peregra was significantly attracted or arrested by all test chemicals, and P. contortus by all chemicals except acetate. P. fontinalis was strongly attracted to acetate, propanoate, butanoate and maltose, but not to the longer chain acids. P. planorbis was attracted or arrested by Carbon-3 to Carbon-8 carboxylic acids but did not respond to maltose and was repelled by acetate. B. tentaculata was attracted only to propanoate and maltose, and was repelled by acetate. P. vortex responded only to the Carbon-8 carboxylic acid. Experiments involving L. peregra and butanoate showed that, although repeated stimulation tended to reduce total attractant and arrestant indices, response levels were still significant up until the 5th test. Response levels could be enhanced by increasing exposure concentration (minimal thresholds 0.01-0.1 mM), increasing pH (minimal threshold pH 6.0), and by food deprivation. These findings are discussed with reference to the distribution of British freshwater snails and their feeding niches.